The present invention relates to an apparatus and a method for producing an optical data recording medium provided with a recording layer formed of an organic dye type recording material.
Recently, there has been developed an optical disc using an organic dye as the recording material whereby the productivity is improved by using a rotary coating method, i.e. a spin coating method, for producing a film.
Japanese Patent Unexamined Publication 61-129747 shows a conventional technique related to the spin coating method. This manufacturing technique is available for a recording material layer having an average film thickness in the range of from 0.035 to 0.14 micron. In this technique, control of the film thickness is carried out only by the RPM of the spin coat and concentration of the coating solution.
Also, there has been known an optical data recording disc on which a recording layer is formed of an organic dye type heat mode recording material. Since the recording layer of this optical data recording disc may be formed by the spin coating method, the manufacturing equipment therefor may be simplified in comparison with the case of using a vacuum film forming machine. Also, it is advantageous that the spin coating method leads to a high productivity.
FIG. 47 of the illustrations is a perspective view showing one example of a conventional spin coating apparatus to be used for producing such a kind of an optical data recording discs. A substrate 102 is horizontally mounted on a vertically placed rotary spindle 101. A nozzle 104 with a tip end 103 is arranged above a substrate 102 and the top end 103 is bent vertically toward the substrate 102 The nozzle 104 is held so that its tip end 103 may be moved from an inner circumferential portion to an outer circumferential portion of the substrate 102 as desired. The tip end 103 of the nozzle 104 is moved from the inner circumferential portion to the outer circumferential portion of the substrate 102 and simultaneously therewith a predetermined amount of a layer or film forming material is injected from the nozzle tip end 103, whereby the film forming material is coated uniformly on the substrate 102.
At present, the CD (compact disc) for reproducing music has been widely used. Since, however, the CD is used for reproduction only and does not have a so-called DRAW (direct read after write) function, a user cannot make a recording on such CDs or edit them. There is thus a strong demand for a CD having this DRAW function. Further, in the case of an optical disc having applications other than as a CD, a less expensive optical disc including the DRAW function is desired.
A metal material such as Te for a void type medium or a metal material such as In for a so-called phase changing type medium effecting dislocation from crystal to non-crystal is known to be used as an optical recording material having the DRAW function. Since, however, a recording layer composed of these metal type recording materials is formed by using a thin film formation technique such as a vapor-deposition method, a sputtering method or the like, there remains problems in mass-productivity and cost.
Thus, the spin coating method is considered to be desirable in increasing the productivity for forming a film.
As the spin coating method, there is a method for supplying material in a center of a disc by gravity, a downflow method, and a method for dropping material on an intermediate portion in a doughnut shape and removing extra material (Japanese Patent Examined Publication 61-5794).
The central dropping method is shown in FIGS. 48 and 49 in which a solution 105 is dropped in the central portion of the substrate 102 of the disc-like optical recording medium (FIG. 48), and immediately thereafter, the substrate is rotated at a high speed to thereby remove an excess of the solution 105 by the centrifugal force to form a film (FIG. 49).
In the downflow method, the nozzle is linearly moved from the outer periphery to the inner periphery (or from the inner periphery to the outer periphery) of the substrate 102, while rotating the substrate to drop the solution 105 and remove an excess of solution 105 to form a coating layer.
As shown in FIGS. 50, 51 and 52, in the high speed removing method, under the condition that the substrate 102 is initially rotated at a low speed or held in a stationary position, the solution 105 is dropped onto a portion around a clamp area A of the substrate. Thereafter, the substrate 102 is rotated at a high speed so that the excess of the solution 105 is removed from the substrate to form a coating layer.
Also, in the case where the coating liquid layer of the recording material is formed on prepits (having a width of 0.4 to 0.5 micron and a depth of about .lambda./4, where .lambda. is the wavelength of light) copied on a replica surface (copied layer) of a surface of the substrate 102 or pregrooves (guide grooves having a width of about 0.4 to 0.5 micron and a depth of about .lambda./8) by the spin coating method, or in the case where a coating liquid for a protective layer is applied, by the spin coating method, to the recording layer surface of the recording layer which has been dried to form a film, it is well known that the coating liquid layer formed by the spin coating or the coating layer formed after drying the recording layer is kept in the states shown in FIGS. 53 and 54.
Namely, it is known that a recess 110 of the prepit or the pregroove is filled with the recording layer material 3 so that no recess is formed in either the recording layer 3 or the protective layer 8a, or otherwise the recess is formed in the recording layer 3, but no recess is formed in the protective layer 8a.
In addition to the instant application, the present applicants have filed U.S. Appln. Ser. No. 367721 on Jun 19, 1989 and U.S. Appln. Ser. No. 380295 on Jul. 19, 1989.
According to the technique disclosed in the above-described Japanese Patent Unexamined Publication 61-129747, it is very difficult to control the thickness or uniformity of the film only by the RPM of the spin coat and the concentration of the coating solution. For example, in the case where a low boiling point solution is selected, evaporation of the solution is roped during the spin coating, to form a non-uniform film. Furthermore, a difference in film thickness between the inner and outer peripheral portions of the optical disc will lead to a change in the reflection factor or transparency to cause a tracking error or the like.